Critical Nucleation Effects on the Structural Relationship Between ZnO Seed Layer and Nanowires

Abstract

The effects of the structural morphology of the ZnO thin seed layer composed of nanoparticles grown by dip coating have been investigated on the structural properties of ZnO nanowires grown by chemical bath deposition. It is revealed by scanning electron microscopy that the growth of ZnO nanowires is limited by the mass transport of chemical precursors in solution, leading to the inverse relationship of their average diameter and length with their density. It is shown by transmission electron microscopy and X-ray diffraction measurements that ZnO nanowires epitaxially grow on the seed layer and preferentially nucleate on the free surface of ZnO nanoparticles. The vertical alignment of ZnO nanowires as quantitatively deduced by X-ray pole figures is found to be improved by strengthening the texture of the seed layer along the c axis. Similarly, their density increases, showing that the c polar plane is highly reactive chemically and presents preferential surface nucleation sites. The relationship between the average diameters of ZnO nanoparticles and nanowires is completely driven by the nature of the nucleation site that is strongly dependent upon the growth conditions and upon the structural morphology of the seed layer. The texture, roughness, and porosity of the seed layer are three critical parameters.

Physical Properties of Annealed ZnO Nanowire/CuSCN Heterojunctions for Self-Powered UV Photodetectors

“…The structural properties of ZnO NWs strongly depend on the structural morphology of the ZnO seed layer, such as nanoparticle size, density, orientation, polarity, and porosity. 12,13 The growth conditions in the chemical bath such as the nature of chemical precursors and related concentrations, pH, and additives are also crucial for controlling the structural morphology of ZnO NWs. 7−11 Owing to the expected increase in light harvesting 14 and extraction efficiency, as well as charge carrier management, the integration of ZnO NWs has recently been achieved in optoelectronic and photovoltaic devices such as light emitting diodes 15 and nanostructured solar cells.…”

The Effect of a Sputtered Al-Doped ZnO Seed Layer on the Morphological, Structural and Optical Properties of Electrochemically Grown ZnO Nanorod Arrays

“…As shown, both nanorod diameter and height were found to be proportional to 1/N, in very good agreement with the theoretical modeling. Thus, we conclude that: i) the characteristic dimensions of ZnO NRs such as their average diameter and length are completely driven by their density, 46 and ii) the ZnO NR growth process is indeed mass transport limited.…”

“…32,48 Thus, the radial growth of ZnO NRs on the seed layer is also limited by the ZnO nanoparticle size in the nucleation step in addition to the mass transport of chemical precursors in solution in the growth step. 46 Nevertheless, the coalescence of neighboring nucleation sites from close-packed grains, during a second step, cannot be totally excluded. 32 In the present case, the 200 nm mean diameter value exhibited by the ZnO NRs grown onto the bare FTO/glass substrate can be correlated with the FTO particle size values (ca.…”

“…50 As in the case of ZnO NRAs fabricated by chemical bath deposition, the ZnO NRAs growth by electrodeposition should be limited by the mass transport of the chemical precursors in solution. 46 In fact, as being the zinc ion in the electrolytic solution present at very low concentration values (1 mM), electrochemical growth process (at these ED potential values), will be mass transport limited. That is, it is expected that the average diameter and length of ZnO NRs are strongly related to their density (N).…”

“…The c-polar plane chemical reactivity has been found to be favorable for the growth of ZnO NRs in solution, and hence these planes may present preferential surface nucleation sites. 46 Figure 7 shows typical X-ray diffraction patterns of the ZnO NRAs obtained by electrodeposition on a naked FTO/glass substrate and onto different AZO thin film seed layers grown at different growth times (t SL ) onto an FTO/glass substrate as indicated, as well as the standard reference powder diffraction pattern for hexagonal ZnO. The X-ray diffraction peaks can be indexed to the hexagonal wurtzite ZnO structure (JCPDS file No.…”